1. Field of the Technology
The present application relates generally to mobile stations and network selection methods employed thereby.
2. Description of the Related Art
A mobile communication device, such as a cellular mobile station, may be capable of making and receiving telephone calls and/or sending and receiving data over a wireless communication network. Before it is able to do this, the mobile station selects and registers with one of a plurality of communication networks which are available within its geographic coverage area. After registering with the selected network, the mobile station operates in an idle mode where it “camps-on” a particular wireless communication channel of the network to monitor for calls or messages. “Network selection” is the particular process performed by the mobile station for selecting the one communication network through which to register and operate.
Cellular telephony operation and network selection schemes are documented in standards specifications that govern the behavior of cellular mobile stations and associated systems. One well-known cellular standard is the Global System for Mobile Communications (GSM) standard. GSM 03.22/European Technical Standards Institute (ETSI) TX 100 930, Technical Specification (TS) 23.122 from the 3rd Generation Partnership Project (3GPP), and other related standards specifications describe the many details of cellular operation and network selection. These documents describe how a mobile station behaves as it moves and roams between various regions and countries to maintain coverage with networks (referred to as Public Land Mobile Networks or PLMNs), primarily for the purpose of providing continuous telephone service.
Traditionally, a mobile station performs network selection by initially scanning to identify all available communication networks within its surrounding coverage area. Each network is identified by a unique Mobile Country Code (MCC) and Mobile Network Code (MNC) pair. If the “home network” (HPLMN) of the mobile station is available, the mobile station will ordinarily select and operate with the home network. If the HPLMN is unavailable, the mobile station will ordinarily select and operate with the communication network having the highest priority in a preferred network list stored in memory of the mobile station. There may be several preferred network lists, commonly referred to as Preferred PLMN lists (PPLMN lists), stored on a Subscriber Identity Module (SIM) card of the mobile station. For example, the PPLMN lists may include a user-controlled PPLMN (U-PPLMN) list and an operator-controlled PLMN (O-PPLMN) list. The above-described network selection method is commonly referred to as an “automatic” network selection method. As an alternative to this automatic selection method, an end-user of the mobile station may be provided with the ability to manually select from a plurality of listed available networks which are visibly displayed on the mobile device. This conventional network selection method may be referred to as a “manual” network selection method.
Some issues exist with conventional network selection techniques for a mobile station, particularly relating to operation with the HPLMN. After recovering from an out-of-coverage condition, a mobile station operates to select the PLMN with which it had just previously registered (i.e. its “RPLMN”). If the RPLMN is unavailable, the mobile station performs a scan to identify and select a PLMN which may be the HPLMN. However, the specifications do not clearly and specifically address the situation where the RPLMN is not the HPLMN of the mobile station. If the RPLMN is not the HPLMN, and the HPLMN is available after the recovery from the out-of-coverage condition, it is specified that the mobile station is limited to selecting the non-home RPLMN (if available) upon recovery. Such conventional operation is described in ETSI specs 3.22/23.122. Similar problems exist when the mobile station is powered off while operating with the RPLMN and subsequently powered back on. In a related issue, the standards specify that if the last RPLMN is unavailable while the mobile station is in “manual” mode, the mobile station shall camp on any network providing emergency service. This selected network may not be the optimal network with which to operate, especially, for example, if the home network is available.
Accordingly, there is a resulting need for network selection methods and apparatus that overcome the deficiencies of the prior art.